Cache lowercase aliases for action/plugin matching

[multiplex55]

Motivation

• Reduce per-search heap allocations and repeated to_lowercase() calls by caching lowercase alias strings for folders and bookmarks.
• Keep UI search results correct immediately after alias file changes by rebuilding both original and lowercase alias maps on watch events.

Description

• Added parallel lowercase alias maps folder_aliases_lc and bookmark_aliases_lc to LauncherApp and helper builders folder_alias_maps() / bookmark_alias_maps() to load both original and pre-lowercased alias values in one pass.
• Introduced normalize_alias() and alias_matches_lc() helpers to centralize alias normalization and case-insensitive matching logic used by search paths.
• Updated initialization in new() to populate both alias maps and updated process_watch_events() to refresh both maps on WatchEvent::Folders and WatchEvent::Bookmarks, calling search() after refresh to update visible results.
• Reworked search_actions() and search_plugins() to use the cached lowercase alias maps via alias_matches_lc() instead of calling to_lowercase() inside tight loops, while continuing to use the existing action_cache for lowercase label/desc checks.
• Added unit tests that assert (1) action search remains case-insensitive when using cached lowercase aliases and (2) watch events refresh both original and lowercase alias caches for folders and bookmarks. (Tests are in src/gui/mod.rs.)

Testing

• Ran cargo fmt --all which completed successfully.
• Attempted cargo test for the added unit(s), but the build failed in this environment during dependency compilation due to a missing system library required by alsa-sys (pkg-config/alsa.pc not available), so the new tests could not be executed here.
• Verified code changes and new tests were added and cargo fmt applied; the search behavior and alias-refresh logic are covered by the new unit tests for environments where system build deps are present.

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Codex Task